I. Field of the Invention
The present invention relates to methods for manufacturing push rod balls for use in various devices such as internal combustion engines. More particularly, this invention pertains to streamlined processes for push rod ball manufacture and to a novel push rod ball and push rod assembly.
II. Brief Description of Relevant Art
Push rod balls are necessary for accurate and efficient function of the internal combustion engines, hydrostatic pumps and motors, compressors, etc. These balls range in size from diameters of approximately 2 mm to 12 mm. Push rod balls are generally composed of suitable durable metallic materials such as steel, steel composites such as CPM 10V and the like. The push rod ball is fastened to the hollow shaft of the push rod by means of a suitable weld. The push rod ball has through bore which extends diametrically through body of the push rod ball and is positioned such that the through bore of the push rod ball is positioned on the same center line as the push rod shaft. The push rod ball through bore assists in fixturing during assembly and provides a lubricant passage through the unit.
Because of the constant wear and abrasion on the surface of the push rod ball, it is necessary to provide a durable external wear surface. An appropriate wear surface can provide increased part life and performance.
As presently manufactured, the rough manufactured balls are sorted according to size and then headed to orient the balls for subsequent processing. The balls are subjected to a soft grinding operation to provide essentially spherical geometry. After soft grinding, the essentially spheroid metal balls are carburized and hardened by maintaining the metal balls in a natural gas environment at a temperature of 1700.degree. F. (926.6.degree. C.) for an appropriate interval after which the balls are water quenched and laboratory inspected to ensure the efficiency and completeness of the carburization and hardening processes. The carburized hardened balls are annealed at a temperature between 1600.degree. F. and 1800.degree. F. (871.degree. C. and 982.degree. C.) in an oil bath and tumbled to clean. After an additional inspection, the annealed balls are drilled in an automatic drilling process to produce the appropriate through bore. The drilled balls are subjected to another tumble cleaning process and dried then rehardened to repair any micro fractures or imperfections which may have been initiated in the exterior surface as a result of the drilling process. The rehardening process involves introducing the drilled balls into contact with a nitrogen-rich environment at a temperature above 1600.degree. to 1800.degree. F. (871.degree. C. and 988.degree. C.) along with subsequent oil quenching. The rehardened balls are subjected to finish grinding and polishing processes.
The resulting push rod balls have the cross-sectional profile as generally shown in FIG. 3. The push rod balls have a soft core with a hardened case region proximate to the outer wear surface. The hardened case region extends through the ball to the through bore at the regions adjacent to the openings of the through bore.
It can be appreciated that the conventional process is energy and labor intensive. Additionally, the amount of handling and processing necessary to produce functional push rod balls provides opportunity for processing imperfections and push rod ball parts which must be rejected for non-compliance with desired manufacturer specifications. The push rod units manufactured with push rod balls produced by conventional processes exhibit a particular failure mode due to weakened or ineffective connection at the junction between the push rod and push rod ball. Without being bound to any theory, it is believed that this is due to the difficulty of achieving an effective weld to the through hardened material of the push rod ball.
It has been widely held in the relevant art that push rod ball manufacturing processes required each of the enumerated steps to produce functional, durable push rod balls. An alternate method of manufacturing push rod balls which results in long lasting durable components while providing savings in labor and/or energy costs or the costs related to handling steps would be highly desirable. It is also desirable to provide a push rod ball which can be welded to the push rod in a manner which eliminates or decreases the number of improper weldments or failures in the push rod unit.